On occasion, other species of filarial worms may infect humans. These are species most often seen in wild or domestic animals. The disease state is known as zoonotic filariasis.
In humans, Dirofilaria (dog heartworm) causes a pulmonary and cutaneous nodule disease; microfilaremia occurs rarely.
Dirofilaria immitis is found worldwide and transmitted to humans by a mosquito bite. In these cases, the humans are considered accidental hosts, whereby (according to CDC)44:
- The infective larvae migrate to the human heart and die.
- Any dead worms may lodge inside a pulmonary artery, causing tissue death (infarcts) or blockage/nodules.
- Symptoms are chest pain and cough.
- A nodule in the lung is called a "coin" lesion on X-ray, and is commonly asymptomatic.
Other species may cause subcutaneous lesions in humans45:
- Dirofilaria tenuis (raccoon parasite in the USA)
- Dirofilaria ursi (bear parasite in Canada)
- Dirofilaria repens (dog/cat parasite in Europe, Africa, and Asia)
Lastly, the following can also infect humans:
- Animal species of Onchocerca
- Animal species of Brugia
Diagnosis is usually made by finding adult worms in sections of tissue.
45. Heymann DL. Control of Communicable Diseases Manual. 21st ed. APHA Press. 2022.
46. CDC/Green. Image #21126. "Under a magnification of 1125X, this photomicrograph depicted the head region of a Dirofilaria immitis microfilaria." PHIL public domain. Created 1968. Accessed April 6, 2023. https://phil.cdc.gov/Details.aspx?pid=21126
